I Am A New Mommy Of A 5 Month Old

I am a new mommy of a 5 month old girl. She has been rolling over on her tummy and back to her back consistently for two weeks. When I lay her down at night she is on her back and often rolls over onto her tummy. I am afraid of SIDS and want to ensure she is well in her sleep. Should I turn her back over on her back or leave her alone?